Walther Benzinger

Crystallization Fouling in Experimental Micro Heat Exchangers—Optical and Thermal Investigations

The intention of this work is the basic investigations of the fouling behavior in micro heat exchangers. Therefore fouling experiments with calcium carbonate (CaCO3) in an experimental micro heat exchanger were carried out and observed with a digital microscope. The investigations included local temperature measurements confirmed by computational fluid dynamics simulation as well as optical visualization of the fouling process inside the microchannels. The detected fouling resistances R f were in the range of 10−5–10−4 m2 K W−1. Cleaning in place was possible and also optically observed.

Modeling Fouling Factors for Microscale Heat Exchangers

This article presents an approach to the modeling of CaCO3 fouling and cleaning in a microscale cross-flow heat exchanger. The fouling progress was detected by thermal, fluid dynamical, and optical measures. In general, the observed fouling phenomena at microscale were comparable to those at macroscale. The detected thermal fouling resistance was between 10− 6 and 10− 3 m− 2 K− 1. As expected, crystallization fouling strongly depends on the surface temperature. In addition, the surface coverage can be a useful measure for both processes—fouling and cleaning. An extended approach to derive a reasonable fouling allowance was formulated through a fractional fouling resistance.

Influence of Deposits by Crystallization Fouling in Microchannels on the Heat Transfer Performance of Micro Heat Exchangers

In the last few years many new microstructured devices were developed and manufactured for different applications in chemical industry and for process engineering. However, the use of micro structured devices in the chemical industry is still rare in spite of the potential benefits these devices offer. One essential reason for the limited use of micro structured devices could be the intrinsic advantage of these structures: the small dimension. In applications of micro structured devices it might be possible that the microchannels get blocked by contaminations in the fluid or that deposition (fouling) could induce flow restrictions in the microchannels. Fouling is defined as the deposition of material on surfaces, e.g. by chemical reactions or phase transition due to the crystallization of inversely soluble ions. This can yield in a reduction of the cross section of the microchannels up to total blocking. Furthermore, fouling can cause a degradation of the heat transfer performance, an increase of the pressure drop in the device, a change of the fluid distribution in the micro structure and a shorter residence time of the fluid. Experimental investigations concerning crystallization fouling in micro structures were carried out at the Institute for Micro Process Engineering (IMVT) of the Karlsruhe Institute of Technology (KIT) and at the Institute for Chemical and Thermal Process Engineering (ICTV) of the Technische Universitat Braunschweig. The intention of these investigations is the development of experimentally verified and generally applicable correlations to describe the crystallization fouling in micro heat exchangers.Copyright